The main aim of this research is to clarify some of the mechanism underlying porphyrin metabolism. A mechanism was proposed for the biosynthesis of uroporphyrinogens from porphobilinogen on the basis of the interaction among 2-aminomethyldipyrrylmethanes and 2-aminomethyltripyrranes and the porphobilinogen polymerizing enzymes. The research will be developed further after we have prepared by synthesis the corresponding 2-aminomethylbilanes and we examined their interaction with the enzymatic system. We have not found yet any enzymatic incorporation of the bilanes into uroporphyrinogens. The studies with porphobilinogen oxygenase - the new enzyme of the porphyrin pathway which we have recently discovered - allowed its isolation from human erythrocytes. The fluctuations of this enzyme in normal blood were established, as well as its decrease in samples of blood of porphyric or anemic persons. A study of this oxygenase as well as skatole pyrrolooxygenase and tryptophan pyrrolooxygenase in different plant materials was carried out. It was found that the three enzymes showed isoenzyme forms, which differed in their cationic charge.